Typically, electric vehicles convert the power collected from an overhead wire into three-phase AC power by an inverter circuit and drive main motors by supplying this AC power to the main motors, thereby obtaining a propulsion force. For example, in the case of a DC overhead wire, the typical configuration is such that the DC power supplied from the overhead wire is converted into variable-voltage variable-frequency AC power by an inverter circuit and the main motor is driven by using this AC power. Moreover, in the case of an AC overhead wire, the typical configuration is such that the AC power supplied from the overhead wire is converted once into DC power by a converter circuit, this DC power is further converted into variable-voltage variable-frequency AC power by an inverter circuit, and the main motor is driven by using this AC power.
Moreover, in the control of the main motor for a railway vehicle, in order to minimize the switching loss of the inverter circuit, a one-pulse mode, in which a rectangular wave voltage is output by switching only twice over an electrical angle of 360° of the AC-voltage-command fundamental wave and the voltage to be output to the main motor is fixed to a maximum voltage, is used in accordance with the speed range (for example, see Patent Literature 1).
On the other hand, a main motor is composed of a stator and a rotor. The circuit configuration of a stator winding is typically related to the losses in the main motor. For example, when the stator winding is composed of parallel circuits, it is known that a circulating current is generated in the stator winding depending on the relationship between the number of parallel circuits and the number of poles (for example, see Patent Literature 2).